linux-ext4 - Re: [PATCH 2/2] ext4: introduce ext4_get_group

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Message-ID: <20130327031207.GC5861@thunk.org>
Date:	Tue, 26 Mar 2013 23:12:07 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Lukas Czerner <lczerner@...hat.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH 2/2] ext4: introduce ext4_get_group_number()

On Mon, Mar 25, 2013 at 11:24:11AM +0100, Lukas Czerner wrote:
> Currently on many places in ext4 we're using
> ext4_get_group_no_and_offset() even though we're only interested in
> knowing the block group of the particular block, not the offset within
> the block group so we can use more efficient way to compute block group.
> 
> This patch introduces ext4_get_group_number() which computes block group
> for a givem block much more efficiently. Use this function instead of
> ext4_get_group_no_and_offset() everywhere where we're only interested in
> knowing the block group.

Again, we have the same problem as the previous patch.  I could
imagine setting a flag which uses the shift-instead-of-div
optimization, but that will reduce the optimization somewhat.  OTOH,
an 64-bit division is pretty expensive, especially on older/simpler
CPU's, so perhaps it's worth it.

   	  	      		    	    - Ted
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